This invention relates generally to the field of turbine inspections, and more specifically to an apparatus for inspecting the discs of a turbine rotor assembly.
High reliability of power generation equipment is an ongoing goal of the electric utility industry. Turbine parts are routinely inspected during planned plant outages in order to detect operationally induced discontinuities before they progress to a point where they may risk component failure. One portion of the turbine that is routinely inspected is the blade root area of the turbine rotor assembly.
A prior art steam turbine rotor assembly 10 is illustrated in cross-sectional view in FIG. 1. The rotor assembly 10 includes a shaft 12 on which are mounted a plurality of wheels or discs 14 that are coaxial with the shaft 12, with the shaft 12 extending through a bore formed at the center of each disc 14. A plurality of blades 16 are mounted to the periphery of each disc 14, generally by inserting a root portion of the blade (not shown) into a mating groove 18 formed along the circumference of the disc 14, as shown in FIG. 2. It is known to scan the disc web surface 20 with an ultrasonic transducer or other type of sensor in order to search for cracks in the region of the groove 18. Such prior art inspections are normally conducted with the rotor assembly 10 removed from the turbine casing and supported on a test stand at an inspection location. The ultrasonic sensor is mounted on an elongated arm that is manually guided between adjacent blades 16 to position the sensor against the disc web surface 20 while the rotor assembly 10 is slowly rotated on the test stand. One may appreciate that such manual positioning of the sensor is strenuous and subject to the potential for positional inaccuracy. Accordingly, an improved scheme for positioning the sensor during a turbine rotor disc inspection is desired.
An apparatus for positioning a sensor proximate a surface of a disc of a turbine rotor assembly is described herein as including: a sensor assembly; and an alignment correction assembly supporting the sensor assembly from a support surface and providing passive freedom of movement there between.
An apparatus for positioning a sensor proximate a surface of a disc of a turbine rotor assembly as the rotor assembly is supported over a support surface is described herein as including: a means for supporting a sensor in a vertical direction; and a means for providing a passive freedom of movement between the sensor and the support surface about a horizontal plane.
A turbine rotor inspection apparatus is described herein as including: a base; a first sled supported vertically on the base and free to move in a first direction along a horizontal plane; a theta alignment assembly supported vertically on the first sled and free to rotate in the horizontal plane; a second sled supported vertically on the theta alignment assembly and free to move in a second direction perpendicular to the first direction in the horizontal plane; a vertical drive assembly supported by the second sled and having a selectable vertical length; a head assembly connected to the vertical drive assembly; and a sensor connected to the head assembly.